With growing use of computers, a need to use more memory cells to store large amounts of data has increased. In general, memory cells have rows, columns and blocks that can store data. However, during manufacturing and fabrication, portions of a memory array may be found defective (e.g., row, column, block or any combination thereof). During wafer testing defective rows, columns or blocks are replaced with redundant rows, redundant columns and redundant blocks.
One method to remedy defective rows, columns and blocks is to replace them with a redundant row, a redundant column and a redundant block memory cells. This method uses on-pitch fuses to disable a defective row, a defective column and/or a defective block respectively. For example when a defective row is detected, the on-pitch fuse is blown in order to disable the defective row and row control circuitry is used to enable a redundant row to replace the defective row. Similarly when defective columns or when a defective block is detected, the on-pitch fuse for the block containing the defective columns is blown to disable the block containing the defective columns. Similarly, the on-pitch fuse for the defective block is blown to disable the defective block. When this defective block or block containing defective columns is disabled, block control circuitry enables a redundant block to replace the disabled block.
The on-pitch fuse method for replacing defective rows, columns and/or blocks is shown in FIG. 1. Unfortunately this method adversely affects the size of the memory array since on-pitch fuses are physically placed for every row and in some cases for every block in the array. Placing the fuse in the array substantially increases the die size. Moreover, this method leads to a slower redundancy operation because it requires critical signals that control the redundant rows, columns and/or blocks to be generated through additional circuitry in the fuse latch, affecting the speed of the redundancy operation.
Another method for replacing defective rows, columns and/or blocks is to use off-pitch fuses in conjunction with control logic. Unfortunately, not only does this method require using complex control logic it also adversely impacts the speed for the redundancy array section.